Synthesis and characterization of nano-sized LiFePO4 cathode materials prepared by a citric acid-based sol–gel route

Abstract

LiFePO₄/carbon composite cathode materials were synthesized by a sol–gel process. The citric acid in the developed sol–gel process plays the role not only as a complexing agent but also as a carbon source, which improves the conductivity of the composites and hinders the growth of LiFePO₄ particles. Nano-sized LiFePO₄ particles without the impurity phase were successfully synthesized. The grain size of LiFePO₄ particles in the range of 20–30 nm is obtained at calcined temperatures from 450 to 850 °C. Increasing the calcination temperature leads to a decrease in the carbon content but an increase in the conductivity of the composites in the range of 400–850 °C. However, the conductivity slightly decreases if the calcination temperature further increases to 950 °C. The LiFePO₄/carbon composite synthesized at 850 °C shows the highest conductivity (10⁻³ S cm⁻¹), the highest specific capacity, and the best rate capability among the synthesized materials. It is worthy to note that the cell performance of the LiFePO₄ depends on the electrochemical cycling procedure employed.